This invention relates to a method for reactivating spent catalyst. The method is generally applicable to the reactivation of any porous, crystalline catalyst material used in any hydrocarbon conversion operation wherein such catalyst eventually becomes inactive through the accumulation of carbonaceous residue within its pores, or channels. The term "porous" as used herein is intended to apply to such materials having pore openings not greater than about 15 angstroms and more generally possessing pore openings within the range of from about 4 to about 8 angstroms.
The method of this invention is especially useful in reactivating any of a variety of porous, crystalline metallophosphate catalysts and metallosilicate zeolite catalysts encountered in such refinery operations as cracking, conversion of methanol to gasoline, conversion of olefins to gasoline and distillate range hydrocarbons, isomerization, disproportionation, reforming, hydroforming, hydrotreating, hydrodewaxing, and the like. At some time during the use of the catalyst, the accumulation of carbonaceous residue within the pores, or channels, of the catalyst reaches the point where its further use becomes impractical. The thus spent catalyst must then be subjected to reactivation treatment to restore its activity. Typically, reactivation of the spent catalyst involves contact with hydrogen at temperatures ranging from 900.degree. F. to 1000.degree. F., high hydrogen flow rates (about 25,000, SCF/bbl cat-hr) and contact times of 24 hours or so. However, hydrogen reactivation does not always completely restore the original level of activity of the catalyst. For example, it has been observed that following hydrogen reactivation of an HZSM-5 catalyst, the loss in cycle length for a catalytic dewaxing operation was substantially less than the original cycle length. The number of days the catalyst can remain on stream decreases from cycle to cycle and eventually continued reactivation becomes impractical.
While air (oxygen) regeneration can be effective to rid the catalyst of hydrocarbon residues, a decrease in cycle length has also been observed. Where the catalyst contains a metal component, e.g., a hydrogenation-dehydrogenation noble metal such as platinum or palladium and/or a base metal such as nickel, air regeneration can result in still other problems such as metal sintering and agglomeration.